Cold start engine exhaust emissions is a key component for overall vehicle emission control. During the cold start, it may be difficult to achieve full combustion during the crank and run up on an engine and still maintain the minimum emission requirements. Specifically, direct injection gasoline engines may have several unique issues during starting, such as larger variation in injection rail pressure and/or more limited air and fuel mixing. Further, unlike port injection, most all of the fuel injected is present in the cylinder, and therefore if not combusted it may leave the engine as unburnt hydrocarbons.
One approach to address cold start direct injection performance includes injecting on the intake stroke during a first combustion event, and then injecting during the compression stroke for subsequent events. For example, U.S. Pat. No. 7,047,945 describes such operation.
However, for intake stroke injection on the first combustion event, the large amount of injected fuel tends to travel across the combustion chamber and hit the opposite wall depending on the injector targeting. The fuel remaining on the wall generally does not combust. Likewise, one drawback for compression stroke injection during cranking, even after the first combustion cycle, is that the cloud of fuel (which may be rich) may not be repeatably and tightly controlled, and as such the cloud location can miss the spark plug.
Therefore, engine starting may be addressed by a method for starting an internal combustion engine having direct fuel injection into a cylinder, comprising only for a first combustion event under selected conditions during an engine start, directly injecting fuel to the cylinder at least twice, where each of said two injections at least partially occur during a compression stroke.